A site where you can see the various focal

Forgive the title, but I did not know how to summarize my request!
In practice it for days I try a site that I found several months ago, where it was possible, on a variety of photographs, see the different angles of view regarding the various focal lengths.
That was a photo taken with an ultra wide angle and then were given the varying focal lengths to realize the difference in field of view.
This site I can not find it!
Can anyone help me?